1. Field of the Invention
The present invention relates to a liquid ejecting apparatus. More particularly, the present invention relates to a liquid ejecting apparatus that makes liquid discharged from openings of a nozzle plate mounted on a liquid ejecting head adhere to recording material.
2. Description of Related Art
When a liquid ejecting apparatus makes liquid adhere to recording material without leaving blank space on the peripheral border of the recording material, the liquid ejecting apparatus anticipates unavoidable displacement between the recording material and a liquid ejecting head so that the liquid is ejected over a region slightly wider than the dimension of the recording material. For this reason, the liquid is discharged to an area, on which the recording material is not located, in the neighborhood of both side edges and upper and lower ends of the recording material. Thus, in order to prevent surplus liquid from flying in all directions and contaminating the periphery, an absorbing member is arranged at a position facing the liquid ejecting head in the direction in which the liquid is discharged to cause the absorbing member to absorb the surplus liquid not adhered to the recording material.
In addition, recording material may extend and crease by adhering liquid over the material. At this time, when the extended recording material contacts with the absorbing member by bending of the material due to wrinkles, the recording material is adhered to the liquid, which has already been absorbed in the absorbing member, to be contaminated. Thus, in anticipation of the extension of the recording material, a gap of around 2 to 4 mm is provided between the recording material and the absorbing members in the liquid ejecting apparatus. In addition, an interval of around 1 mm is provided between the liquid ejecting head and the recording material.
On the other hand, upon request of resolution improvement of a recording image, a recent liquid ejecting apparatus miniaturizes droplets discharged from openings of a nozzle plate to the degree of several pl. Since such a minute droplet has extremely small mass, a droplet, which has once been discharged, rapidly loses kinetic energy due to viscous resistance of an atmosphere. Specifically, the velocity of a droplet less than, e.g., 8 pl reaches generally zero after the droplet flies around 3 mm in the atmosphere. A minute droplet losing kinetic energy takes a balance between falling motion by acceleration of gravity and viscous resistance force of an atmosphere, and thus requires long time up to termination of falling.
In addition, in the case of a distance of 3 to 5 mm obtained by adding the gap between the nozzle plate and the recording material to the interval between the recording material and the absorbing member, the discharge velocity of the liquid ejecting apparatus for a droplet of 3 pl is set highly in order to transfer the droplet from the nozzle plate to a surface of the absorbing member. However, viscous resistance of the atmosphere acting on the droplet further increases so as to reduce travel distance on the contrary.
On the other hand, the discharge velocity of the liquid ejecting apparatus is set highly in order to transfer the droplet by 3 to 5 mm obtained by adding a gap between the liquid ejecting head and the recording material and a gap between the recording material and the absorbing member. However, an influence of viscous resistance of the atmosphere acting on the droplet of about 3 pl further increases so as to reduce travel distance on the contrary.
Moreover, when the discharge velocity is high, an extremely minute droplet referred to as satellite ink generated when the droplet leaves the nozzle plate is easy to be generated.
Furthermore, the liquid ejecting apparatus periodically repeats an operation referred to as flushing. The flushing is an operation of sending a driving signal to the liquid ejecting head in a state that the recording material is not in the apparatus, so to speak, to attack liquid. By such an operation, liquid having increased viscosity is removed from a nozzle with a little discharge volume. However, since liquid discharged during this flushing is consumed for only flushing and thus does not contribute to recording to the recording material, a small droplet is discharged to save consumption of liquid. Moreover, since time required for flushing reduces throughput of an original recording operation, liquid is discharged from all nozzles in the shortest time in the flushing. In such a flushing operation, a large quantity of satellite ink is generated.
Most of satellite ink generated as a result of various events as described above becomes aerosol floating in the vicinity of a traveling area of the liquid ejecting head. A part of the aerosol floats to the outside of the liquid ejecting apparatus and adheres to the perimeter of the liquid ejecting apparatus. Moreover, most of aerosol adheres to each portion in the liquid ejecting apparatus before long. Especially, when aerosol adheres on a carrying path of recording material such as a platen, recording material to be next carried is contaminated. Furthermore, when aerosol adheres to an electric circuit, a linear scale, various optical sensors, and so on of the liquid ejecting apparatus, malfunction of the apparatus may be caused. Moreover, when a user touches a part to which aerosol adheres, a hand of the user is also contaminated.
Japanese Patent Application Publication No. 2004-202867 discloses a liquid ejecting apparatus including a function of collecting the aerosol actively.
A liquid ejecting apparatus disclosed in this patent document includes an absorbing member that is arranged at a position facing a nozzle plate in order to absorb surplus liquid that does not adhere to recording material. Moreover, one electrode is a metallic component arranged on a surface of the absorbing member, and the other electrode is a nozzle plate made of metal having openings for discharging liquid. When voltages different from each other are applied to these electrode and nozzle plate, an electric field is formed between them. Moreover, droplets discharged from the nozzle plate in such a liquid ejecting apparatus are charged with electricity to be the same electrode as that of the nozzle plate when being discharged from the nozzle plate. For this reason, since droplets floating as aerosols are charged with electricity, the droplets head for an electrode without being decelerated by coulomb force acting between the droplet and an electric field, and are adsorbed to the electrode having the polarity opposite to that of the droplets. The droplets adsorbed to the electrode are absorbed by a capillary phenomenon, and are finally absorbed in the absorbing member.
The above-described apparatus has applied an extremely high voltage in order to form an electric field for collecting aerosol. For example, the Japanese Patent Application Publication No. 2004-202867 discloses that a 3-kilovolt voltage is applied in order to obtain the electric field. This voltage is equivalent to generating an electric field of 1 MV/m assuming that a distance between the nozzle plate and the absorbing member is 3 mm.
Moreover, in order to form an effective electric field between the nozzle plate and the absorbing member in the above-described liquid ejecting apparatus, a corresponding voltage between them, e.g., several hundred volts or more is applied. In the case of an ink-jet type recording apparatus that is an example of a liquid ejecting apparatus, when forming an electric field of the degree of 80 kV/m effective for collecting satellite ink, the voltage of around 350V is applied between the nozzle plate and a recording material side electrode. If the nozzle plate is a ground level, it is expected that a 350-volt voltage is applied to the recording material side electrode. Therefore, for example, when a user puts his/her hand in the apparatus and touches the recording material side electrode in order to remove a jammed recording material, possibility of an electric shock is high. Moreover, when changing a liquid cartridge, a user may reluctantly put his/her hand in a case. In this case, the user may also touch an electrode to which a high voltage is applied without discretion and thus receive an electric shock.